1. Field of the Invention
The present invention relates to an industrial two-layer fabric having uniform dehydration characteristics throughout the fabric without causing closing of the mesh openings thereof which will otherwise occur at weaving portions of binding yarns.
2. Description of the Related Art
Fabrics made by weaving warps and wefts have heretofore been used widely as industrial fabrics and they are, for example, papermaking fabrics, conveying belts, and filter cloths. They are required to have fabric properties suited for using purposes or using environments. Requirements for papermaking fabrics to be used in a papermaking step for removing water from raw materials by utilizing meshes of the fabrics are especially strict.
For example, there is a demand for fabrics that have excellent surface smoothness and therefore do not easily transfer a wire mark of the fabrics to paper, fabrics having a sufficient dehydration property to completely and uniformly remove excess water contained in the raw materials and having sufficient rigidity and wear resistance for suitable use of them even under severe environments, and fabrics capable of maintaining conditions necessary for making paper of a good quality for a long period of time.
There is also a demand for fabrics having a fiber supporting property, capable of improving a papermaking yield, having size stability, and having running stability, and the like.
The demand for papermaking fabrics has become severe with a recent increase in the speed of a papermaking machine.
Among industrial fabrics, papermaking fabrics must satisfy the most severe requirements so that a description on them will promote understanding of the requirements for most of the industrial fabrics and solutions of them. Therefore, they will hereinafter be described using papermaking fabrics as one example.
With a recent increase in the speed of a papermaking machine, papermaking fabrics are required to have a particularly excellent dehydration property and surface smoothness. Although dehydration characteristics differ with the type of a machine employed or the type of a product to be manufactured, a uniform dehydration property is one of essential conditions for any product.
Further, it becomes more difficult to satisfy the demand for papermaking fabrics because an increase in a mixing rate of minute fibers in raw materials as a result of recent increased use of waste paper causes insufficient dehydration so that sufficient and uniform dehydration has gained in importance.
When water to be dehydrated is retained in the fabric upon papermaking, it swashes on the wet paper and becomes a defect. A method of decreasing a mesh thickness is employed with a view to reducing water retention. An example of a flat yarn is shown in U.S. Pat. No. 5,379,808.
FIGS. 2, 5, and 8 of U.S. Pat. No. 5,379,808 are plan views illustrating three examples. They are examples of a two-layer fabric having a binding yarn for weaving an upper side weft and a lower side weft. The warp binding yarn is woven with a lower side weft in the lower layer and with an upper side weft in the upper layer. It forms a weaving portion in parallel with a knuckle of an upper side warp.
The fabric has no lower side warps. It can suppress occurrence of a defect on paper during papermaking by using flat yarns or laying two small-diameter warp binding yarns in parallel to decrease a mesh thickness and thereby decreasing a water retention amount of the mesh. Since the weaving portions of warp binding yarns on the upper side are parallel with the knuckles of upper side warps so that the mesh openings are narrowed with the binding yarns only at these portions. Such a change in water drainage property sometimes results in production of paper having an uneven thickness.
Japanese Patent Laid-Open No. 2004-68168 shows a two-layer fabric having pairs of an upper side warp and a warp binding yarn with a view to achieving a uniform dehydration property. This fabric has a uniform design on the surface thereof by using an upper side knuckle of warp binding yarns for weaving upper and lower layers and an upper-side warp design in combination. Although the fabric can keep its design because the two warps cooperatively form, on the surface thereof, a design corresponding to one warp, they form intersections and at the same time, the knuckles of warp binding yarns do not completely move on the line of upper side warps but are present in parallel therewith. Mesh openings are therefore clogged at portions where knuckles of warp binding yarns exist, which may cause a partial change in the dehydration property and inevitably provide paper with a watermark.